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Allele-specific malE mutations that restore interactions between maltose-binding protein and the inner-membrane
1Department of Microbiology, College of Physicians and Surgeons, Columbia University, New York, NY 10032.
Abstract:
Active accumulation of maltose and maltodextrins by Escherichia coli depends on an outer-membrane protein. LamB, a periplasmic maltose-binding protein (MalE, MBP) and three inner-membrane proteins, MalF, MalG and MalK. MalF and MalG are integral transmembrane proteins, while MalK is associated with the inner aspect of the cytoplasmic membrane via an interaction with MalG. Previously we have shown that MBP is essential for movement of maltose across the inner membrane. We have taken advantage of malF and malG mutants in which MBP interacts improperly with the membrane proteins. We describe the properties of malE mutations in which a proper interaction between MBP and defective MalF and MalG proteins has been restored. We found that these malE suppressor mutations are able to restore transport activity in an allele-specific manner. That is, a given malE mutation restores transport activity to different extents in different malF and malG mutants. Since both malF and malG mutations could be suppressed by allele-specific malE suppressors, we propose that, in wild-type bacteria, MBP interacts with sites on both MalF and MalG during active transport. The locations of different malE suppressor mutations indicate specific regions on MBP that are important for interacting with MalF and MalG.
Insights
Escherichia coli uses maltose-binding protein (MBP) to transport sugars across its membranes. Specific mutations in MBP restore transport, revealing key interaction sites with MalF and MalG proteins.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Escherichia coli actively transports maltose and maltodextrins using a complex system involving outer and inner membrane proteins.
- The maltose transport system includes LamB (outer membrane), maltose-binding protein (MalE, MBP), and inner membrane proteins MalF, MalG, and MalK.
- Previous studies established MBP's essential role in transporting maltose across the inner membrane.
Purpose of the Study:
- To investigate the interaction between MBP and inner membrane proteins MalF and MalG.
- To characterize malE mutations that restore maltose transport in malF and malG mutants.
- To identify specific regions on MBP crucial for interaction with MalF and MalG.
Main Methods:
- Utilizing malF and malG mutants with impaired MBP interaction.
- Analyzing malE mutations that restore proper MBP interaction with defective MalF and MalG.
- Assessing the allele-specific restoration of transport activity by malE suppressor mutations.
Main Results:
- Identified malE suppressor mutations that restore maltose transport activity in a manner dependent on the specific malF and malG alleles.
- Demonstrated that both malF and malG mutations can be suppressed by allele-specific malE mutations.
- Mapped the locations of malE suppressor mutations to specific regions on MBP involved in MalF and MalG interaction.
Conclusions:
- Propose that in wild-type E. coli, MBP interacts with both MalF and MalG during active maltose transport.
- Conclude that specific regions on MBP are critical for mediating interactions with MalF and MalG.
- Highlight the allele-specific nature of these interactions, providing insights into the maltose transport mechanism.